Field of the Invention
Preferred example relates to the art of a selectable one-way clutch adapted to selectively enable torque transmission only in one direction and to interrupt torque transmission in both directions.
Discussion of the Related Art
One example of a one-way clutch used in a hybrid vehicle is described in Japanese Patent No. 5120650. In the hybrid vehicle taught by Japanese Patent No. 5120650, an outer race of the one-way clutch is connected to a motor-generator, and an inner race of the one-way clutch is connected to a casing. According to the teachings of Japanese Patent No. 5120650, the outer race is allowed to rotate relatively with the inner race in the forward direction, but inhibited to rotate relatively with the inner race in the counter direction. The motor-generator may be uses as a starter of the engine.
A conventional selectable one-way clutch is adapted to selectively enable torque transmission only in one direction. To this end, in the selectable one-way clutch, a selector plate interposed between a pocket plate and a notch plate is rotated by an electromagnetic actuator or the like to selectively provide an engagement between the selector plate and the pocket plate. The selectable one-way clutch of this kind may also be used in the hybrid vehicle taught by Japanese Patent No. 5120650 instead of the one-way clutch.
In order to reduce friction, lubrication oil is applied to friction sites between the pocket plate and the selector plate, and between the selector plate and the notch plate. However, if viscosity of the oil is too high, the selector plate may be rotated unwillingly by a drag torque or a shearing force resulting from a rotation of the notch plate. For this reason, the pocket plate may be brought into engagement accidentally with the notch plate if temperature is extremely low.